A position detection system configured to detect a position of a user in a room is applied to a variety of fields. For example, JP-A-2004-301380 discloses an air conditioning system capable of locally air-conditioning a vicinity of a user by arranging a plurality of tag readers on a matrix in a room to thus detect a position of the user with precision. However, when detecting a position of a user with the air conditioning system disclosed in JP-A-2004-301380 in a building having a plurality of floors, a tag carried by the user and a tag reader provided for a floor adjacent to a floor at which the user exists, are enabled to communicate with each other. As a result, a misdetection that the user exists at a floor different from the floor at which the user actually exists occurs.
FIG. 9 is a schematic view showing a misdetection that a user exists at a floor different from a floor at which the user actually is in the background art. A tag reader 200b mounted on a ceiling 400b of a corresponding floor performs communication with a tag carried by a user 402 existing at the corresponding floor, thereby detecting a position of the user. However, as shown in FIG. 9, a signal arriving range of the tag reader 200b extends to not only the corresponding floor but also an adjacent floor. Thus, if a user carrying a tag 100 is at the adjacent floor, the tag 100 detects a leakage signal to the adjacent floor, which is generated from the tag reader 200b, so that a misdetection is caused.